1. Field of the Invention
The present invention generally relates to testing equipment and methods and, more particularly, toward a method and device for testing deformation of sheet metal parts.
2. Description of Related Art
In stamping processes to form metal parts, such as automobile body panels, various stamping parameters may have an effect on the resulting metal parts"" strength or resistance to deformation. For example, the cushion or stamping pressure used in forming the metal part is directly related to the resistance to deformation of the metal part. However, the optimum cushion pressure, as it relates to deformation resistance, is variable and depends upon many factors, including the curvature or profile of the metal part. Moreover, other factors, such as the location and distribution of internal body panel supports, have a significant affect on the body panel""s resistance to deformation. Therefore, it is desirable to test the body panels at various locations to determine their resistance to deformation. In the past, testing for resistance to deformation has been a manual operation whereby a worker applies a predetermined load and visually determines the resulting deformation. As such, the conventional method is inherently inexact, and provides results that vary from worker to worker.
Other methods and devices for testing metal parts have been developed, typically for small parts that are intended to have a certain elasticity, such as flexible electrical contacts. For example, U.S. Pat. No. 6,082,201 teaches a method and device for imposing a predetermined amount of permanent deformation on a heat treated part. The ""201 patent teaches placing the flexible contact in a testing jig, contacting a manually-operated load imposer on the flexible contact to establish a set point, and then manually moving the load imposer toward the flexible contact to deform the flexible contact. A displacement measuring unit measures the amount the load imposer is displaced and, when a predetermined amount of displacement is measured, the movement of the load imposer is terminated and the flexible contact, while being held in the deformed condition by the load imposer, is subjected to heat treating.
Following heat treating, the ""201 load imposer is manually rotated to release pressure on the flexible contact and, when the load imposer is disconnected from the flexible contact, an final set point is determined. The difference between the initial set point and the final set point is the amount of permanent deformation resulting from the heat treating.
Accordingly, there exists a need in the art for a method and device for automatically testing a sheet metal part to determine the part""s resistance to deformation. There further exists a need in the art for a method and device for testing metal parts to detect localized weaknesses.
The present invention is directed toward a method and device for testing sheet metal parts to determine the part""s resistance to deformation. The present invention is further directed toward a method and device for detecting localized weakness in metal parts as part of an overall method for identifying areas requiring remedial strengthening measures.
In accordance with the present invention, a device for testing a metal part for deformation includes a support, a motor secured to the support, a shaft that is moved longitudinally by the motor, a load cell for detecting pressure applied to the metal part, a displacement measuring device for measuring deformation of the metal part, and a controller. The shaft has a dimple head secured thereto for engagement with the metal part. The controller activates the motor to move the dimple head toward and away from the metal part based upon pressure sensed by the load cell.
In further accordance with the present invention, a method for testing a sheet metal part for deformation includes moving a dimple head forwardly toward a test point on the metal part, determining when the dimple head encounters resistance to movement, and measuring displacement of the dimple head when resistance to movement is encountered to establish a first reference displacement value. The dimple head is moved forwardly into the metal part until a predetermined pressure is detected. The displacement of the dimple head when the predetermined pressure is detected is measured to establish a second reference displacement value. Maximum deformation of the metal part at the test point is calculated by subtracting the first reference displacement value from the second reference displacement value.
In further accordance with the inventive method, after the predetermined pressure is detected, the dimple head is moved rearwardly and displacement of the dimple head is measured as the dimple head is moved rearwardly. When the displacement is less than or equal to the first reference displacement value, the dimple head is again moved forwardly. Thereafter, it is determined when the dimple head encounters resistance to movement and the displacement of the dimple head when resistance to movement is encountered is measured to establish a third reference displacement value. A permanent deformation value of the metal part at the test point is determined by subtracting the first reference displacement value from the third reference displacement value.